U.S. Pat. Nos. 2,429,584; 3,537,987; 3,610,600; 3,820,767; 3,904,180; 3,972,709; 4,067,731; and references therein are among the numerous patents illustrating that filtering and degasing of molten metal are generally well known in the art. The in-line use of disposable porous ceramic foam filters for filtering molten aluminum are shown in U.S. Pat. Nos. 4,007,923; 3,917,242; 3,893,917; 3,962,081 and 4,092,153. A continuous filter for molten copper is disclosed in U.S. Pat. No. 4,277,281.
Since molten metal filters of the type shown in U.S. Pat. No. 4,277,281 are partially or completely submerged in molten metal during the filtering process, it is not possible to determine the effectiveness of the filter without analysis of the cast product resulting from the filtered melt. Since considerable time is required for the filtering, laundering, casting, rolling, cooling and analysis processes, a great deal of contaminated metal is processed before the defective filtering is realized. Typical defects which can result in insufficiently filtered metal are filters which are cracked or otherwise damaged during shipment, handling or installation and filters which are not properly fitted in the tundish or filterbowl. Cracks in such filters tend to open during preheating or operation which allows unfiltered metal to pass through the system, causing unacceptably high inclusions. During normal operation, the filter gradually becomes clogged, resulting in a considerable head difference between the entrance side of the filter and the exit side of the filter. A normal head is expected in the filtering process and is relied upon in the filtering process to maintain proper metal flow rate required for casting. However, where a crack is present in the filter, a normal head build up is not present and cannot be relied upon to control metal flow, and improper filtration results. In addition, where the molten metal filter becomes overly clogged, insufficient metal flow results.
The present invention solves these problems by providing an apparatus for indicating the effectiveness of a molten metal filter to prevent undue restriction of flow and to prevent production of an insufficiently filtered metal product.